Hi, the Troll looks really small more like a goblin or something, its mainly to do with the size of the head I think. Creatures heads stay generally the same size as you scale the rest of them up, so a large troll would have a smaller head compared to the rest of its body. I would also spend some time practicing anatomy, do some quick sculpts copying from books or photos so you can get more knowledge on it overall. Just some thoughts, anyway Keep going man!